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Volume 6, Issue 1, Pages 69-78 (July 2007)
Dissociation of Hepatic Steatosis and Insulin Resistance in Mice Overexpressing DGAT in the Liver Mara Monetti, Malin C. Levin, Matthew J. Watt, Mini P. Sajan, Stephen Marmor, Brian K. Hubbard, Robert D. Stevens, James R. Bain, Christopher B. Newgard, Robert V. Farese, Andrea L. Hevener, Robert V. Farese Cell Metabolism Volume 6, Issue 1, Pages (July 2007) DOI: /j.cmet Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 1 Generation of Liv-DGAT2 Mice
(A) DNA construct for generating Liv-DGAT1 and Liv-DGAT2 mice. Expression of the human DGAT cDNA is driven by the APOE promoter/enhancer sequences. (B) DGAT2 mRNA levels in tissues of Liv-DGAT2 mice. Total (mouse and human) DGAT2 mRNA levels were measured by real-time PCR. Tissues were from 12- to 14-week-old male mice (n = 6–9) on an ad libitum chow diet. ∗p < versus WT. In this and all other figures, error bars represent ±SEM. (C) Increased DGAT2 protein levels in livers of Liv-DGAT2 mice. Homogenate samples (100 μg) were analyzed by SDS-PAGE and immunoblotting. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 2 Hepatic Steatosis in Liv-DGAT2 Mice
(A) Livers from 13-week-old male mice. (B) Levels of triacylglycerol (TG), diacylglycerol (DG), and ceramides in tissues of Liv-DGAT2 mice. Lipid content of tissues was measured in 12- to 15-week-old male mice (n = 6–10) on an ad libitum chow diet. ∗p < 0.05, ∗∗p < versus WT. (C) Levels of fatty acyl-CoAs in livers of Liv-DGAT2 and Liv-DGAT1 mice. Fatty acyl-CoAs were measured in livers of 12- to 15-week-old male mice (n = 7–10) on an ad libitum chow diet. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < versus WT. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 3 Hepatic Expression of Lipogenic, Oxidative, and Gluconeogenic Genes in Liv-DGAT2-Low and Liv-DGAT2-High Mice mRNA levels were quantified by real-time PCR in 12- to 14-week-old male mice (n = 6 per genotype) on an ad libitum chow diet. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < versus WT. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 4 Glucose and Insulin Metabolism in Male Liv-DGAT2-Low and WT Mice on a Chow Diet (A) Glucose tolerance tests (GTT). Glucose was administered intraperitoneally after an overnight fast, and blood glucose was measured at the indicated times. Mice were 10–12 weeks of age; n = 12 per genotype. (B) Insulin tolerance tests (ITT). Insulin was administered intraperitoneally after a 4 hr fast, and blood glucose was measured at the indicated times. Mice were 10–12 weeks of age; n = 21 WT mice and 19 Liv-DGAT2-low mice. (C–E) Hyperinsulinemic-euglycemic clamp studies. The rates of glucose infusion (C), hepatic glucose production (D), and insulin-stimulated glucose disposal (E) were measured during constant insulin infusion at 2 mU/kg/min. Mice were 20 weeks of age; n = 7 per genotype. (F) Increased phospho-PKB/Akt (Ser473) in livers of mice after hyperinsulinemic-euglycemic clamp studies. Control mice received injections of saline. (G–I) Insulin signaling in Liv-DGAT2-low mice. Saline or insulin was administered intraperitoneally to chow-fed 15- to 17-week-old male mice after an overnight fast. Livers were excised and snap frozen in liquid nitrogen after 2 min to measure PI3K activity (G) (n = 5 for each group) and after 15 min to measure PKCλ/ζ activity (n = 5 per group) (H) and total PKB/Akt and phospho-PKB/Akt (Ser473) (I). For (I), a representative blot is shown. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 5 Phenotype of Liv-DGAT1 Mice
(A) DGAT1 mRNA levels in liver and skeletal muscle of Liv-DGAT1 mice and lipogenic gene mRNA levels in liver of Liv-DGAT1 mice. Total (mouse and human) DGAT1 mRNA and lipogenic gene levels were measured by real-time PCR. Tissues were from 12- to 14-week-old male mice (n = 5–6) on an ad libitum chow diet. ∗p < 0.05, ∗∗p < versus WT. (B) Hepatic levels of TG, DG, and ceramides in 12- to 15-week-old male Liv-DGAT1 mice (n = 7–10) on an ad libitum chow diet. ∗∗p < versus WT. (C) Glucose tolerance tests. Glucose was administered intraperitoneally after an overnight fast, and blood glucose levels were measured at the indicated times. n = 19 WT and 12 Liv-DGAT1 mice. (D) Insulin tolerance tests. Insulin was administered intraperitoneally after a 4 hr fast, and blood glucose was measured at the indicated times. n = 22 WT and 15 Liv-DGAT1 mice. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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Figure 6 Inflammatory and ER Stress Markers in Liv-DGAT1 and Liv-DGAT2 Mice Representative immunoblots of liver homogenates from 12- to 15-week-old male mice are shown for phospho-JNK (Thr183/Tyr185) and total JNK, phospho-NF-κB p65 (Ser536) and total NF-κB, and phospho-PERK (Thr980). Because a specific antiserum for detecting total PERK was unavailable, GAPDH was used as a loading control for quantification of phospho-PERK. Liver homogenates from WT mice fed a high-fat diet for 16 weeks served as positive controls. Bands were quantified by densitometry (n = 4–6). ∗p < 0.05, ∗∗p < 0.01 versus WT. Cell Metabolism 2007 6, 69-78DOI: ( /j.cmet ) Copyright © 2007 Elsevier Inc. Terms and Conditions
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